I need to know how I would go about fixing my speedometer problem. It is about 10 MPH off. When Im driving, if im going 40 MPH, IM really doing 50. So what caused this problem? I think its connected to the tranny gears isn't? Please help. I dont know if I need to replace the speedometer cable or what. Thanks.

86 trans am

is this a new problem or did you buy the car with the problem, sounds like someone changed the rear end ratio and never changed the speedo to compensate. there is a set of small gears that are in the side of the tranny which connect to the speedo cable, i'm not sure about the calculation but I know someone on here can tell you which gears to buy from GM to fix the problem,its pretty easy to do once you have the new gears.